The present invention relates to the field of percutaneous transluminal coronary angioplasty (PTCA). In particular, the present invention is a non-over-the-wire dilatation balloon catheter.
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating certain types of vascular diseases. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Typically, the catheter is introduced and directed partially through a patient's vascular system via a guide catheter. Using fluoroscopy, a physician guides the catheter through that portion of the patient's vascular system distal of the guide catheter until the balloon is positioned across the stenosis. While the catheter is being steered through the vascular system, the balloon is in a deflated state, wrapped (i.e., folded) tightly about the distal end of the catheter to reduce the profile of the balloon. Reducing the profile of the balloon allows the catheter to easily travel through the guide lumen of the guide catheter and traverse arterial vessels and stenoses having small through openings. Once the catheter is positioned with the balloon across the stenosis, the balloon is inflated by supplying fluid under pressure through an inflation lumen to the balloon. Inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to re-establish an acceptable blood flow through the artery.
Over-the-wire catheters and non-over-the-wire catheters are two types of dilatation catheters that are commonly used in angioplasty. An over-the-wire catheter has an inflation lumen and a guide wire lumen through which a separate guide wire is advanced to establish a path to the stenosis. Since the guide wire is separate from the catheter, torque applied to the guide wire to steer the guide wire through the vascular system and across the stenosis is not conveyed to any part of the catheter. Once a distal end of the guide wire is across the stenosis, the separate over-the-wire catheter is advanced over the guide wire until the balloon is positioned across the lesion.
One type of non-over-the-wire catheter has its own built in guide wire (sometimes referred to as a core wire) which is joined to a hypotube, such that the core wire, balloon and inflation lumen comprise a single unit. Due to this single unit construction, torque (i.e., a rotational force) applied to a proximal end of a hypotube of the non-over-the-wire catheter (to which the core wire is fixedly attached) to steer the catheter through the vascular system and across the stenosis, is conveyed to other parts of the catheter.
In particular, torque induced rotation applied to the hypotube and core wire combination is transmitted to a distal end of the balloon and to a proximal end of a waist tube that extends about the core wire and couples the hypotube to the balloon. However, due to the tortuosity of portions of the guide catheter and of the patient's vascular system, the balloon and the waist tube may contact parts of the walls of the guide catheter guide lumen and the arterial vessels. This contact may cause rotation of portions of the balloon and the waist tube to lag behind rotation of the hypotube and core wire combination. The lag in balloon rotation dampens steering responsiveness of the balloon catheter itself, since contact of the balloon with the walls of the guide lumen and arterial vessels imparts drag to the distal end of the core wire. This, in turn, dampens the responsiveness of the core wire distal spring tip.
Typically, a spring tip is provided at the distal end of the core wire and is formed with a J-bend. The J-bend permits the balloon catheter to be steered into desired arterial branches. That is, torque induced rotation applied to the hypotube is transmitted to the spring tip through the core wire to position the J-bend to enter the desired arterial branch. A non-uniform ability to accurately position the J-bend of the spring tip, such as may be caused by a lag in balloon rotation which dampens steering responsiveness, makes the balloon catheter difficult to steer and may unnecessarily prolong the angioplasty procedure.
In addition, the lag in balloon rotation causes the balloon and the waist tube to twist upon themselves. The balloon tends to twist upon itself proximally from its distal attachment to the core wire, while the waist tube twists upon itself distally from its proximal attachment to the hypotube. If balloon twist is minimal, as a result of minimal steering torque applied to the hypotube, the balloon will untwist upon application of inflation fluid pressure to inflate the balloon once the balloon is positioned across a stenosis. However, if balloon twist is significant, the balloon may not inflate uniformly. Non-uniform balloon inflation exhibits balloon behavior wherein portions of the balloon (i.e., constrictions in the balloon due to twist) do not inflate to their maximum diameter. These under-inflated constrictions do not uniformly press the stenosis into the arterial wall and hence, do not effectively dilate the lesion to allow acceptable blood flow through the arterial vessel. In addition, upon deflation of the balloon, those segments of the balloon (i.e., segments adjacent the constrictions) which were fully inflated may not completely deflate. These partially deflated segments may make withdrawal of the balloon catheter from the patient's vascular system back through the guide catheter difficult.
It is desirable in a non-over-the-wire catheter to reduce the transmission of torque (applied to the hypotube and core wire combination) to the balloon of the catheter. The reduction in torque transmission would abate twisting of the balloon as the catheter is steered through the vascular system, and thereby permit uniform inflation and deflation of the balloon which is needed to effectively dilate the stenosis to re-establish an acceptable blood flow through the arterial vessel. In addition, the reduction in torque transmission, from the core wire to the balloon, would reduce, if not eliminate, the twisting of the balloon from the lag in balloon rotation upon the application of torque to the core wire. This reduction in balloon twist would alleviate steering difficulties sometimes associated with non-over-the-wire catheters wherein torque is readily transmitted from the core wire to the balloon.